A gate electrode of a dynamic random access memory (DRAM) is also used as a word line. In order to decrease resistance of the word line, a part of the gate electrode is formed of a metal film. However, it is known that as a line width of the word line becomes smaller, resistivity of the metal film increases due to a thin line effect. As a result, the resistance of the word line increases, and variations in resistance of word lines become larger. The increase of the resistivity due to the thin line effect becomes particularly notable when the line width is 30 nm or less.